Lampholders are widely used and generally have bayonet and screw types, the first one being matched with a bayonet bulb and the second one being matched with a screw bulb. There exists a potential risk of using such a lampholder in which metal parts are live when a bulb is not fixed into the lampholder and a power switch remains in the connected state. The lampholder is accessible to hands and fingers because it has a relatively large diameter, resulting in an electric shock accident.
Chinese Patent No. ZL91215869.7 provides a safety dual-purpose base for both screw and bayonet bulbs, which is provided with movable rods beneath positive and negative conducting pieces and with insulating washers above positive pole contact and bayonet negative pole contact. Chinese Patent No. ZL93225663.5 discloses a two-purpose anti-electroshock lamp base for screw and bayonet bulbs, which is fitted with an insulating washer between a conducting rod extending from the base and a spread spring so that the conducting rod is not in direct contact with positive and negative conducting pieces. Another safety dual-purpose base for both screw and bayonet bulbs is known from Chinese Patent No. ZL93226038.1, with an improvement in a bayonet slot of the base, the bayonet slot being formed as a rectangular slider capable of sliding within a bayonet trunk and having a lateral slot so that when a bayonet bulb is used, the bulb is fixedly inserted in the base. These lamp bases appear to achieve a safety purpose in light of the fact that the contacts are not live when bulbs are not fixed into these lamp bases. However, they still take a risk that an electric shock accident occurs. The accident will happen when a pressure generated by access to elastic metal parts or movable conducting rods with hands or fingers is high enough to cause downward movement of the metal parts or movable conducting rods to turn to an on-state.
International Application No. PCT/CN2003/000546 filed by the applicant relates to a kind of safety lampholder for avoiding accidental electric shock, comprising a screw or bayonet socket, a rooting plate, a conducting piece, an electrical contacting shaft with an round end, a pinpoint pole and a spring switch or a flexing member. The pinpoint pole is fixed in a center positioning base of the lampholder, and the spring switch or the flexing member causes the pinpoint pole to move up and down to form on/off state of a lamp circuit. When a bulb is fixed into the lampholder, the bulb makes the pinpoint pole downward till the spring contacts the pinpoint and the lamp circuit is conducting and the lamp works. When the bulb is removed from the lampholder, the pinpoint moves upward to be reset till the spring is depart from the pinpoint and the lamp circuit is disconnected. When people touch the pinpoint pole capable of moving down only if a given force is applied thereto, it can make people feel pain and stop pressing sequentially, whereby avoiding the accident. Obviously, this kind of safety lampholder is complicated in structure and a number of metal securing members are required for securing or holding the spring switch or flexing member and other parts. Further, a relatively large space is required because the spring moves the same distance as the pinpoint pole in the same direction. This results in complicated construction and high manufacturing costs of the lampholder. Also, the lampholder is of relatively large size and is thus not suitable for being fixed to a position where an ordinary type lampholder is fixed. Disadvantages of inconvenience of fixing the safety lampholder and high manufacturing cost of the safety lampholder make it difficult to be widely used in place of an ordinary type lampholder.